Since the shop has an item limit of 255, all the items have been split into "pages". 
To change which page your game loads, rename the files. 
The file that the game loads is "shopList.slt", so if you rename "shopList_page2.slt" to "shopList.slt", you will load the second page in your game.

More pages have been added to address complaints of missing DLC items, and to future-proof for Iceborne and Master Rank items.

Pages 6 and onwards have not been tested, but are unlikely to have any items in. Feel free to try them yourself if you're curious.
They're there to aid the mod's transition to Iceborne when it is released for PC, as long as the item IDs and files work in the same way.

Expect a fully validated Iceborne update once it is released, but in theory this should work just fine.